This invention relates to a new method of combining continuous filament synthetic yarns of different shrinkage characteristics, particularly a method of combining polyester yarn with drawn polyamide yarn during the polyester yarn drawing process.
In the usual polyester drawtwisting process, undrawn yarn is led from a package placed on a creel to feed rolls which are driven at a constant speed, then across heated metal pins, and then to a take-up godet driven at typically several times the speed of the feed rolls. By this means, the yarn is drawn or extended several times in length for the purpose of moleculary orientating the yarn and developing desired final properties of strength and elongation. From the take-up godet, the yarn may optionally pass through a tangling device and then through a traveler, which rotates around a ring, and onto a pirn which is mounted on a rotating spindle.
In marketing synthetic yarns, there is always a demand for new combinations of yarn which can be processed in a variety of ways. A combination of polyester and polyamide continuous filament yarns would be useful for a number of reasons, one in particular being that by dyeing a knitted or woven fabric made of the combined yarns with suitable dyes, the polyester and polyamide components would be dyed differently, and a "heather" effect from the differential dyeing is obtained. The dyeing characteristics of polyester and polyamide are sufficiently different so that dyeing the combined yarns with the same dye bath can give contrasting colors or a white-and-color effect. Dyeing a combination of two different types of polyester or two different types of polyamide gives only a tone-on-tone effect. From the point of view of a synthetic yarn producer, it would be very desirable to market a combined polyester and polyamide drawn yarn on pirns, ready for texturing, or suitable for knitting or weaving as the next manufacturing step before dyeing.
A prior method of combining polyester and polyamide yarns would be to use a pirn of drawn yarn of each type to supply an end of each yarn to a drawtwister, bypassing the feed roll so no further drawing would take place, winding the yarns around the draw godet, then running the two ends through a tangling or other interlacing device, and finally winding the combined ends on a pirn through use of the ring traveler and lay-rail mechanism in the usual manner.
However, it has been found to be very difficult or impossible to wind combined ends of polyester and polyamide on a pirn in this manner without formation of "loops" in the yarn which makes the quality unacceptable. On unwinding a length of the combined yarn from the pirn, it is found that the polyamide yarn has contracted more than the polyester yarn, causing the yarns to separate. The excess length of the polyester compared to the polyamide causes the loops to form.
Another prior method of combining polyester and polyamide yarn is to place undrawn packages of ech yarn on a doublecreeled drawtwister, combine the ends of yarn, and go through the usual complete drawing process with the combined ends. It has been found that this resulted in the same difficulties as was found with combining two previously drawn ends, as the yarn obtained is still loopy and poorly combined.
The apparent reason for the difficulty in combining different types of yarns such as polyester and polyamide by direct methods is the different shrinkage or contraction which the yarns exhibit after being subjected to tension. In winding from two drawn pirns or drawing from two undrawn packages, the combined yarns are subjected to the same forces by the action of the package-building mechanism such as the traveler and rotating spindle on a drawtwister. After winding on a pirn or other collecting package and then being unwound, the yarn with a greater tendency to shrink, polyamide in the case of a polyester-polyamide combination, will contract enough to cause the combined yarns to separate and form loops.
Attempts have been made to alter the physical properties of the undrawn polyester and polyamide yarns by winding them at different speeds, and by modifying the feed rolls of the drawtwister, in order to have the final physical properties, for example, the orientation and shrinkage of the yarn, match closely enough so that good quality combined yarn is obtained. These attempts have not been successful compared to the results obtained by the method of this invention.
It has been found that with the use of this invention, polyester and polyamide yarns may be combined on a drawtwister to obtain a product of acceptable uniform quality and free of loops.